package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.util.PriorityQueue;
import java.io.IOException;
import java.text.Collator;
import java.util.Locale;

/**
 * Expert: Collects sorted results from Searchable's and collates them.
 * The elements put into this queue must be of type FieldDoc.
 *
 * <p>Created: Feb 11, 2004 2:04:21 PM
 *
 * @since   lucene 1.4
 */
class FieldDocSortedHitQueue extends PriorityQueue<FieldDoc> {

    volatile SortField[] fields = null;

    // used in the case where the fields are sorted by locale
    // based strings
    volatile Collator[] collators = null;

    volatile FieldComparator[] comparators = null;

    /**
     * Creates a hit queue sorted by the given list of fields.
     * @param fields Fieldable names, in priority order (highest priority first).
     * @param size  The number of hits to retain.  Must be greater than zero.
     */
    FieldDocSortedHitQueue(int size) {
        initialize(size);
    }

    /**
     * Allows redefinition of sort fields if they are <code>null</code>.
     * This is to handle the case using ParallelMultiSearcher where the
     * original list contains AUTO and we don't know the actual sort
     * type until the values come back.  The fields can only be set once.
     * This method should be synchronized external like all other PQ methods.
     * @param fields
     */
    void setFields(SortField[] fields) throws IOException {
        this.fields = fields;
        this.collators = hasCollators(fields);
        comparators = new FieldComparator[fields.length];
        for (int fieldIDX = 0; fieldIDX < fields.length; fieldIDX++) {
            comparators[fieldIDX] = fields[fieldIDX].getComparator(1, fieldIDX);
        }
    }

    /** Returns the fields being used to sort. */
    SortField[] getFields() {
        return fields;
    }

    /** Returns an array of collators, possibly <code>null</code>.  The collators
     * correspond to any SortFields which were given a specific locale.
     * @param fields Array of sort fields.
     * @return Array, possibly <code>null</code>.
     */
    private Collator[] hasCollators(final SortField[] fields) {
        if (fields == null)
            return null;
        Collator[] ret = new Collator[fields.length];
        for (int i = 0; i < fields.length; ++i) {
            Locale locale = fields[i].getLocale();
            if (locale != null)
                ret[i] = Collator.getInstance(locale);
        }
        return ret;
    }

    /**
     * Returns whether <code>a</code> is less relevant than <code>b</code>.
     * @param a ScoreDoc
     * @param b ScoreDoc
     * @return <code>true</code> if document <code>a</code> should be sorted after document <code>b</code>.
     */
    @SuppressWarnings("unchecked")
    @Override
    protected final boolean lessThan(final FieldDoc docA, final FieldDoc docB) {
        final int n = fields.length;
        int c = 0;
        for (int i = 0; i < n && c == 0; ++i) {
            final int type = fields[i].getType();
            if (type == SortField.STRING) {
                final String s1 = (String) docA.fields[i];
                final String s2 = (String) docB.fields[i];
                // null values need to be sorted first, because of how FieldCache.getStringIndex()
                // works - in that routine, any documents without a value in the given field are
                // put first.  If both are null, the next SortField is used
                if (s1 == null) {
                    c = (s2 == null) ? 0 : -1;
                } else if (s2 == null) {
                    c = 1;
                } else if (fields[i].getLocale() == null) {
                    c = s1.compareTo(s2);
                } else {
                    c = collators[i].compare(s1, s2);
                }
            } else {
                c = comparators[i].compareValues(docA.fields[i], docB.fields[i]);
            }
            // reverse sort
            if (fields[i].getReverse()) {
                c = -c;
            }
        }

        // avoid random sort order that could lead to duplicates (bug #31241):
        if (c == 0)
            return docA.doc > docB.doc;

        return c > 0;
    }
}
